1. Field of the Invention
This invention relates to a latch assembly that is used to latch and unlatch a door and more particularly to a bored in latch assembly that fits into a standard #161 door preparation used in connection with an exit device.
2. Description of the Related Art
Exit devices are used in many public places to allow people to exit the premises as quickly as possible. Latch assemblies of existing bored in (cylindrical) locksets and latches will bind when a substantial lateral force is applied in the direction of the door swing. In this type of latch assembly a scalp and a face plate bear the load when a lateral force is applied against the latchbolt as the latchbolt makes a transition from an extended position in a strike to a retracted position in a latch tube. When the latchbolt is in the retracted position it allows the door to open. When lateral force is applied while the latchbolt is extended, edges of the scalp and the face plate actually bite into the side of the latchbolt due to the pressure of the edges of the face plate and the scalp against the flat backside of the latchbolt. This causes the latch bolt to bind and therefore not make the transition to the retracted position and prevents the door from opening. These types of latch assemblies will not withstand the lateral forces required by code, specifically ANSI A1563 tests required for all exit devices.
An example of this type of latch assembly can be seen in U.S. Pat. No. 5,947,534 for Panic Exit Device Suitable for Use with Standard Doors issued Sep. 7, 1999 to Zarzycki. The device in U.S. Pat. No. 5,947,534 provides rollers in the exit device mechanism; however, these rollers are inappropriately placed. Because the rollers are inappropriately placed they are not sufficient to relieve the bind that occurs between the latchbolt and the edges of the face plate and the scalp when under lateral pressure.
There is no known apparatus that effectively reduces the bind that occurs between the latchbolt and the edges of the face plate and the scalp which occurs when substantial lateral force is applied in the direction of the door swing.
The present invention solves this problem by extending the latch tube outward and over the edges of the face plate and the scalp creating a continuous bearing surface that enables smooth retraction of the latchbolt.
The present invention provides a bored-in latch assembly for an exit device having a latchbolt inserted within a latch tube, the latchbolt engaging a strike, a face plate adjacent to an end of the latch tube, the end is proximate to the strike, a scalp joined to the face place, the latchbolt moves through the latch tube and enters the strike the improvement comprising a latch tube which extends past the face plate and past at least a leading edge of the scalp where the leading edge of the scalp is adjacent to the face plate, thereby providing a bearing surface for the latchbolt within the latch tube and in which the bearing surface is free of any edges of the face plate and an edge of the scalp which is adjacent to the face plate.
The invention additionally provides for a bored in latch assembly that has a separate bearing sleeve between the latch tube and the latchbolt which supports the latchbolt within the latch tube.
The invention also provides for a bored-in latch assembly which includes roller bearings between the latch tube and the latchbolt which supports the latchbolt within the latch tube.
The invention also provides for a bored-in latch assembly in which the latchbolt has a load reduction angle on the swing side of the latchbolt, the angle is more than 90 degrees as determined from an end of the latchbolt which engages the strike, the angle is measured from the end of the latch tube.